1. Field of the Invention
The present invention relates to a paper guide used with an ink-jet printer and an ink-jet printer having the same, by which when multi-pass printing is performed to improve printing quality of an ink-jet printer, a first printing portion of a paper is flattened and a waveform size of a second printing portion of the paper is reduced.
2. Description of the Related Art
An ink-jet printer includes a paper guide on which a material used in printing e.g., paper supplied from a feed roller is to be placed and flattened. A paper guide rib is provided on the paper guide so as to be parallel with a paper feeding direction.
FIG. 1 is a cross-sectional view schematically illustrating the structure of an ink-jet printer having a conventional paper guide. Referring to FIG. 1, a friction roller 14 contacts a feed roller 10 which receives paper P supplied from a pickup roller (not shown) on a paper path and feeds the paper P by an amount (swath S) which corresponds to a printing area. The friction roller 14 is rotatably connected to one end of a friction roller holder 15, and the other end of the friction roller holder 15 is connected to a printer body. The feed roller 10 comprises a rubber roller 12 coupled to a metal shaft 11, and a gear (not shown) is coupled at an end of the shaft 11 to connect with the power of a driving motor (not shown). The friction roller 14 contacts the circumference of the feed roller 10. The friction roller 14 applies a predetermined pressure to the feed roller 10 by a weight of the friction roller holder 15. If the feed roller 10 is rotated by a driving motor (not shown), the friction roller 14 is rotated by a rotation of the feed roller 10.
An ink-jet cartridge 20 and a paper guide 30 are disposed downstream of the feed roller 10 in a paper path. The paper guide 30 is spaced apart downwardly from a printhead 21 under the ink-jet cartridge 20 by a predetermined gap G, and supports the paper P thereon.
FIG. 2 is a plane view illustrating paper guide ribs 32, illustrated in FIG. 1 in cross-section only, disposed on the paper guide. Referring to FIG. 2, ribs 32 are placed at a predetermined interval I with the interval I spacing from 5–20 mm, and parallel with a paper path. The paper guide rib 32 is formed to a height of about 1–2 mm above the paper guide surface (30a) such that the paper P does not contact directly the surface 30a of the paper guide 30 and supports the paper P to be flattened during a printing.
A plurality of holes 35 are formed in a rear portion of the paper guide 30 downstream of the printhead 21, a paper output roller 40 is placed in each of the plurality of holes 35, and a star wheel 42 is provided on the paper output roller 40.
Printing steps of an ink-jet printer having the above structure will be described in detail with reference to FIGS. 1 and 2.
First, the paper P supplied from the pickup roller (not shown) is fed between the rotating friction roller 14 and the feed roller 10 in a feed direction as illustrated. If the paper P is fed by a friction force between the feed roller 10 and the paper P, the paper P is entered into the paper path by a distance of one swath S at the same velocity as a linear velocity of the circumference of the rubber roller 12. In this case, the paper P is fed toward the printhead 21 and is printed on by the printhead 21, which receives a printing file from a controller (not shown), and ejects ink, and subsequently, printing is performed while the feed roller 10 feeds the paper P by one swath S. If it is determined from the controller that the printing is terminated, the paper output roller 40 outputs the paper P.
However, when multi-pass printing is performed by an inkjet printer having the paper guide having the above structure so as to attempt to print a high-quality image, the feed roller 10 feeds the paper P by a distance of a half-swath S to the paper path. Thus, the swath S may include a front-half part S1 and a rear-half part S2 which each correspond to a half-swath S. After a first printing is performed at the front-half part S1, the paper P is fed by a half-swath S and a second printing is performed on the first-printed portion at the rear-half part S2 in a state when ink on the first-printed portion is not yet dried. Thus, the second printing is performed at a position different from a target position due to an excessive waveform (see the paper P marked by a dotted line W1 of FIG. 5) of the first-printed portion of the paper P at the rear-half part. As a result, printing quality is lowered, and a protruded portion of the first-printed portion of the paper P contacts the printhead 21 and is smeared by the printhead 21.